In the manufacture of integrated circuits (chips) it is well known that it is desirable to encapsulate the chip in order to protected the chip from mechanical damage and contamination. Encapsulation techniques are also known to passivate the chips an enhance their long term performance. There are a variety of well known techniques available for encapsulating chips. These techniques include mounting chips within a cavity of a substrate or a die structure, wire bonding chips to a lead frame and then enclosing the package with a lid. Another technique includes mounting chips to a lead frame, wire bonding the chips to the lead frame and then passivating the chips and a portion of the lead frame in a molded plastic or plastic epoxy body. Yet another technique for packaging and passivating chips includes “flip-chip” bonding to a printed circuit board and then covering the chips with a plastic resin.
There are several applications where the above mentioned packaging and passivation techniques are inadequate because the materials used to form the packaging are opaque and/or do not provide an optical window of suitable quality for optical applications. For example, such packaging is unsuitable for EPROM devices. An EPROM device is a read-only memory device. The program or data which is stored in an EPROM can only be erased through optical radiation (ultraviolet and/or visible) impinging on the surface of the EPROM. Conventional opaque chip packaging does not allow for such a device to be erased optically and, therefore, is unsuitable for packaging these devices. To solve this problem, makers of EPROM devices mount EPROM chips within the cavity of a ceramic package and hermetically seal the assembly with an optically transparently lid.
Micro-electro-mechanical devices (MEM devices) are another class of silicon semiconductors devices. MEM devices are useful for a variety of applications including strain gauges, accelerometers, electronic levels, and also for display light valves or other optical applications. Because of their extremely small moving parts, MEM devices are particularly susceptible to ambient conditions. Accordingly, MEM devices are traditionally sealed within the cavity of a hermetic package to control the operating environment to which the MEM is subjected.
When the MEM device is an optical MEM device, as for example in the case of display applications, the MEM device is required to be accessed optically through the packaging, wherein optical energy penetrates the package, impinges on a surface of the MEM device, and where the optical energy is reflected and/or modulated and then escapes from the package forming the optical image or signal. Though conventional ceramic packages can be hermetic, they also tend to be opaque and are, therefore, unsuitable for use with a variety of optical MEM devices.
A package which includes an optically transparent window can represent a considerable portion of the manufacturing cost for making an optical MEM device. Under certain circumstances it is important to provide a package which has an optical window of suitable optical quality which has a controlled physical relationship relative to another portion of the MEM device, such as a mechanically active portion of the MEM device or the substrate of the MEM device. Specifically, in some applications it is important to position a transparent lid at an angle relative to an optical element or elements of the MEM device to reduce surface reflections from the optically transparent window, where reflections can interfere with the intended image and/or signal.
Conventional silicon semiconductor chip packaging technology does not provide for the ability to control the physical relationship of a transparent window/lid with respect to other portions of a MEM device. Therefore, there is a need for a MEM device with an optical widow that can be controllably positioned at an angle relative to other portions of the MEM device, and in particular at an angle relative the reflective surface(s) of one or more encapsulated optical elements of the MEM device, and a method for making the same.